A combine having an axial-flow rotor assembly is well-known in the art. The rotor assembly of such combines includes a driven rotor which is rotatably and concentrically arranged within a rotor casing. Crop material is fed into a crop receiving forward end of the rotor assembly. A vaned impeller at the forward end of the rotor moves the crop material rearwardly toward a threshing area of the rotor assembly. In the threshing area, the crop material is carried around the rotor by rasp bars which comb the crop material into an annular mat. From the threshing area, the mat of crop material is rearwardly moved to a separating area of the rotor assembly where it is further processed by cooperative instrumentalities on the rotor and rotor casing.
To facilitate the receipt and transfer of crop material through the rotor assembly, a forward end of the rotor casing is provided with a frusto-conically shaped transition section. The vaned impeller at the forward end of the rotor is arranged within the transition section of the rotor casing and includes a series of impeller blades which radially extend outward from the rotor and are provided with a working edge arranged close to the transition section on the rotor casing. The working edge on the blades typically extends from near a forward end to a rearward end of the transition section and in combination therewith defines a narrow annular opening through which the crop material is advanced toward the rasp bars on the rotor.
The impeller blades on the rotor primarily move the crop material rearwardly in a spiral fashion toward the threshing area of the rotor assembly and have minimal effect on combing the crop material into a mat. There is a tendency, therefore, for the crop material to collect into "ropes" or fold into wads as it advances toward the threshing area. The tendency for crop material to collect into a "rope" or fold into a wad is especially pronounced in handling the more difficult crop materials, particularly long straw varieties at high moisture contents and especially rice.
At the rear end of the transition housing, the crop material is presented to a radially extending front face of the rasp bars which tend to cause a "back-feed" problem in the rotor assembly. The "ropes" or folded wads of crop material accentuate the problem by tending to jam or wedge between the rotor and the rotor cage. Such jamming or wedging of the crop material between the rotor and the rotor cage is noisy and can cause serious torque fluctuations in a drive system for the rotor. Occasionally, such jamming will actually prevent the rotor from rotating and may cause serious damage to the drive system. Moreover, such "ropes" or folded wads reduce the threshing and separating efficiency of the rotor assembly due to the undesirable bunching of the crop material.